Molecular switches for organic electronics: A computational approach to oligothiophene-azobenzene hybrids

Molecular switches based on azobenzene (azo) are defined as light-responsive molecules which can change between two configurational states under light stimuli. Responsive azo monolayers can be used to modulate the work function, i.e. they tune the properties of the interfaces – at the electrodes or nanoparticles. In this work, we investigate what happens to the structures, optical properties, and the charge hopping within azo-bithiophene (azo-BT) hybrid monolayers depending on the light stimulus using various computational approaches. Two types of hybrids that differ in the order of azo and BT counting from the anchor group are modelled: azo-BT and BT-azo. One of them (BT-azo) has been studied experimentally by Karpe et al. [1], whose data are used for the model validation. We describe trans- and cis-isomers for each hybrid and conclude that the isomers of BT-azo are more stable. The optical spectra for trans-isomers are similar, whereas the cis-states are characterized by different positions and intensities of the absorption bands. The charge hopping is evaluated for the coupled dimers within Markus-Hush theory of electron transfer.
[1] Karpe S. et al. Chem. Commun. 46 (2010) 3657